Communication systems are designed to transfer information between two devices over a medium in the presence of disturbing influences. Intersymbol interference (ISI) is one well-known disturbing influence in which transmitted symbols become elongated and interfere with adjacently transmitted symbols. This spreading of symbols is generally caused by the low-pass frequency response associated with all communication mediums. Because ISI has the same effect as noise, communication is made less reliable.
One of the most basic solutions for mitigating the effects of ISI is slowing down the speed at which symbols are transmitted over the medium. More specifically, the transmission speed can be slowed down such that a symbol is only transmitted after allowing previously transmitted symbol pulses to dissipate. The time it takes for a symbol pulse to dissipate is called delay spread, whereas the original time of the symbol pulse is called the symbol time. No ISI will occur if the delay spread is less than or equal to the symbol time.
Although slowing down the speed at which symbols are transmitted can eliminate or reduce the effects of ISI, it is generally an unacceptable solution for many of today's communication applications. In fact, many of today's communication applications require speeds in the tens of gigabits per second range. At such high speeds, ISI can completely overwhelm a signal transmitted over relatively small distances for given communication mediums (e.g., a few inches of printed circuit board trace or a few feet of copper cable).
Therefore, a filtering process, referred to as equalization, is often used to flatten the frequency response of a communication medium to mitigate the effects of ISI. Equalization can be applied at the receiver and/or at the transmitter.
The embodiments of the present disclosure will be described with reference to the accompanying drawings. The drawing in which an element first appears is typically indicated by the leftmost digit(s) in the corresponding reference number.